1. Field of the Invention
The invention relates to the improvement of techniques for measuring the flow rate of a thin stream of molten materials such as that of glass, basalts, slag, ceramics and the like, which materials in the molten state are the source of the emission of large-scale radiation.
2. Description of the Related Art
It is known to measure these flow rates by means described in particular in patent SE 82 03650. According to this document, the measuring principle is as follows: two sensors, sensitive to the radiation emitted, are disposed on the path followed by the molten material at a distance from one another. There are irregularities in the emission of the molten material. The sensors are disposed so as to receive the emission from a limited portion of the section of the thin stream in question. The signals received are selected so as to retain only those signals which exceed a given threshold. The conventional technique consists in measuring the time separating the appearance of signals exceeding he threshold on each of the sensors, the measurement being translated into the flow velocity of the material. Measurement of the diameter of the thin stream completes the determination process enabling the flow rate to be attained. The diameter is measured by forming the image of the cross-section of the thin stream on a linear camera and determining the number of radiation sensitive elements of the camera receiving sufficient radiation as corresponding to the width of the thin stream in question.
The arrangements provided in the prior art technique only fulfills the intended aim to a limited extent. In practice, the flow rate measurements are principally used in the control of a regulating die or orifice. The measurements are compared with reference values selected by the operator and any difference relative to these reference values triggers an adjustment of the parameters such as the electrical power supply and consequently the temperature of the die from which the material flows freely. In other words, the flow rate in this type of application has to be measured precisely and continuously since otherwise the system would be totally disorganized.
It is possible to avoid incorrect measurements affecting the regulation process by excluding any measurement which would differ from a high probability variation range defined experimentally. However, this technique is not entirely satisfactory since it results in a systematic loss of data.
The presence of deviant measurements is inherent in the system previously described which is based on the consecutive recognition of two signals exceeding a given threshold by the two sensors. In a system of this type, the identification of the signals cannot be perfect, even if other "safety devices" (in particular those regarding the time separating two signals) enable certain risks of errors to be eliminated.